Are neon transformers installed in an attic permitted? Is lighting required in this space if transformers are permitted?

The answer to both questions is yes. Part (E) of Section 600.31 permits sign transformers in attics as long as there is an opening or access door that provides an opening that is not less than 30 inches by 22.5 inches and a passageway that is not less than 3 feet high and 2 feet wide. Also, a walkway must be provided that is at least 12 inches wide.

Also required is at least one lighting outlet controlled near the point of entry to the soffit or attic space. The requirement for a lighting outlet is new in the 2008 National Electrical Code (NEC).

Disconnects for luminaires

We still are installing wiring and electrical equipment under the requirements of the 2005 edition of the NEC. During an inspection of new construction in an office building, the electrical inspector said disconnecting means must be provided at each fluorescent luminaire. This disconnect must be readily accessible and within sight of the fluorescent luminaires or must be internal to each luminaire. This is a new requirement in the 2008 NEC but not the 2005 edition. Is this a correct interpretation of the 2005 NEC?

Yes, it is. A disconnecting means is required for hazardous locations, indoor installations other than dwellings and accessory buildings, cord-and-plug connected luminaires, some industrial establishments, and emergency luminaires. It also is required where local disconnects supply luminaires from two-wire branch circuits, and disconnects are provided so that the area is not without artificial illumination when a disconnect is turned off. An enforcement date for this requirement and the exceptions was Jan. 1, 2008.

This section, which was 410.73(G) in the 2005 edition, was revised and moved to Section 410.130 in the 2008 NEC. In Section 410.130, the disconnecting means must disconnect the grounded branch-circuit conductor if the luminaire is supplied from a multiwire branch circuit. The words for location of the disconnecting means also are expanded to say that the disconnecting means must be located to be accessible to qualified people before servicing or maintaining the ballast. Also, where the disconnecting means is external to the luminaire, it must be a single device and attached to the luminaire, or the disconnect must be within sight from the luminaire.

Access to electric furnace in attic

Are permanent stairs or a fixed ladder required to extend to the attic in a one-family dwelling unit? The attic contains an electric furnace, a receptacle, a switch and luminaire.

There is no requirement for a permanent ladder or stairs to the attic because it contains an electric furnace, but an accessible disconnecting means for the furnace must be within sight or capable of being locked off by Section 424.19. Working space for this equipment generally is required by Section 110.26 because the furnace may be required to be serviced while energized. Section 110.26 reads, in part: “Spaces About Electrical Equipment. Sufficient access and working space shall be provided and maintained about all electrical equipment to permit ready and safe operation and maintenance of such equipment.” Minimum dimensions of the working space are given in the remaining parts of this section.

AFCI branch-circuit wiring

Is there a maximum length of armored cable permitted to be installed between the panelboard and the arc-fault circuit interrupter (AFCI) device in a residence?

Generally, Section 210.12 requires the installation of combination-type AFCIs at the panelboard to protect the entire branch circuit as it leaves the panelboard, but there are exceptions.

Exception No. 1 to 210.12(B) allows armored cable that complies with 250.118 to be run from the branch-circuit panelboard to the first AFCI device without installing an AFCI at the panelboard. Rigid metal conduit, intermediate metal conduit, and electrical metallic tubing also are permitted wiring methods. However, I am not sure that AFCI-protected receptacles or individual AFCIs are being produced.

The length of armored cable from the panelboard to the AFCI is not limited. It can be any length.

The second exception removes the requirement for AFCI protection for branch circuits supplying fire alarm systems that meet the requirements of Sections 760.41(B) and 760.121(B) where the wiring method is rigid metal conduit, intermediate metal conduit, electrical metallic tubing and Type AC armored cable. Also, all outlet and junction boxes must be metal.

Multiwire branch-circuit disconnect

Does the NEC allow a 14 AWG, three-wire copper NM cable with an equipment ground to supply a disposer and dishwasher in a dwelling unit kitchen? Both appliances have a disconnecting means at the appliances. Can the overcurrent protection be two single-pole circuit breakers?

A 15-ampere multiwire branch circuit is permitted to serve these appliances according to this sentence in Section 210.23: “An individual branch circuit shall be permitted to supply any load for which it is rated.” However, the two single-pole circuit breakers are not suitable without a handle tie. This requirement appears in Section 210.4(B): “Disconnecting means. Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.” Therefore, a two-pole circuit breaker or two single-pole circuit breakers with a handle tie are required at the panelboard where this multiwire branch circuit originates.

Minimum size of conductor at service

What is the minimum size grounded conductor permitted for a 2,000-ampere, 480-volt, three-phase, four-wire service? Does the 12.5 percent rule apply? There are five sets of 500 kcmil Type THHN copper conductors.

The size of the grounded-circuit conductor (may be a neutral) is based on the size of the ungrounded conductors in each raceway. Assuming there are five raceways each containing three-phase conductors and a grounded-circuit conductor, the minimum size grounded conductor is 1/0 AWG copper. This minimum size is required by Section 250.24(C)(2), which reads in part: “Where installed in two or more raceways the size of the grounded conductor in each raceway shall be based on the size of the ungrounded service-entrance conductor in the raceway but not smaller than 1/0 AWG.”

The minimum size grounding-electrode conductor for the service where attached to a grounding electrode not less than 10 feet or buried metal water pipe is 3/0 AWG copper or 250 kcmil aluminum. These sizes are found in Table 250.66.

Many conductors in a raceway

What is the adjusted ampacity of 16 8 AWG copper conductors with Type TW insulation installed in rigid metal conduit? What is the minimum conduit size?

An 8 AWG copper conductor with Type TW insulation has an ampacity of 40, according to Table 310.16. If all branch circuits are three-phase, four-wire and the neutrals do not carry harmonic currents, 12 current-carrying conductors are in the raceway. Not counting the branch-circuit grounded conductor when supplying linear loads is permitted by 310.15(B)(4).

The 12 current-carrying copper conductors must be derated to 50 percent of their table ampacity as shown in Table 310.15(B)(2)(a). This results in a corrected ampacity of 20 (40 × 0.5). The same correction factor and corrected ampacity also applies if the neutral or grounded branch-circuit conductor carries harmonic loads.

If the branch circuits are three-wire, single-phase with one equipment-grounding conductor, there are 10 current-carrying conductors, and the 8-AWG conductors are derated to 20 amperes.

By using Type THHN insulation, the conductors may be derated from 55 amperes as shown in Table 310.16. This results in a corrected ampacity of 27.5.

According to Table C 21C, 8 AWG copper conductors with TW insulation require a minimum 1.5 inches of electrical metallic tubing. The minimum size flexible metal conduit is 1.5, and rigid metal conduit must be at least 1.5 inches. These tables are shown in Annex C of the NEC.

Location of receptacles in dwelling units

Does a receptacle installed above the mantle in a family room in a residence qualify as one of the required receptacles of Section 210.52 of the NEC?

A receptacle installed above a mantel may be counted as one of the required receptacles if it is 5½ feet or less above the floor. Item 5 in Section 210.52 recognizes a receptacle located 5½ feet or less above the floor as one that meets the requirements of Section 210.52(A)(1). A floor receptacle also may be counted as one of the required devices where located within 18 inches of the wall.

Use of circuit breakers as switches

Does the NEC permit a circuit breaker marked SWD as a switch to control high intensity discharge lighting?

No, it does not. Where circuit breakers are used as switches, they must comply with Section 240.88(D), which states: “Used as Switches. Circuit breakers used as switches in 120-volt and 277-volt fluorescent lighting circuits shall be listed and shall be marked SWD or HID. Circuit Breakers used as switches for high-intensity discharge lighting shall be listed and shall be marked HID.”

A circuit breaker with an SWD marking is not suitable for switching HID luminaires.

FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. Questions can be sent to ecmag@necanet.org.